Simulations predict that the first stars in a \Lambda CDM universe formed at redshifts z > 20 in minihalos with masses of about 10 ^ { 6 } M _ { \sun } .
We have studied their radiative feedback by simulating the propagation of ionization fronts ( I-fronts ) created by these first Population III stars ( M _ { * } = 15 - 500 M _ { \sun } ) at z = 20 , within the density field of a cosmological simulation of primordial star formation , outward thru the host minihalo and into the surrounding gas .
A three-dimensional ray-tracing calculation tracks the I-front once the H ii region evolves a “ champagne flow ” inside the minihalo , after the early D-type I-front detaches from the shock and runs ahead , becoming R-type .
We take account of the hydrodynamical back-reaction by an approximate model of the central wind .
We find that the escape fraction of ionizing radiation from the host halo increases with stellar mass , with 0.7 \lesssim f _ { esc } \lesssim 0.9 for 80 \lesssim M _ { * } / M _ { \odot } \lesssim 500 .
To quantify the ionizing efficiency of these stars as they begin cosmic reionization , we find that , for M _ { * } \gtrsim 80 M _ { \odot } , the ratio of gas mass ionized to stellar mass is \sim 60 , 000 , roughly half the number of ionizing photons released per stellar baryon .
Nearby minihalos are shown to trap the I-front , so their centers remain neutral .
This is contrary to the recent suggestion that these stars would trigger formation of a second generation by fully ionizing neighboring minihalos , stimulating H _ { 2 } formation in their cores .
Finally , we discuss how the evacuation of gas from the host halo reduces the growth and luminosity of “ miniquasars ” that may form from black hole remnants of the first stars .